I am also having chimney leaks, but mine are inside the fireplace box, not on the outside. As for leaks inside the fireplace, a roofer came out and advised me my problem might be that the outside of my chimney needs re-pointing. Thats the morter in between the bricks. In time it may come loose an form an open gap. Perhaps that might be one of your problems! I've had two "professionals" try to sell me on the idea of waterproofing but apparently this did not work for you. I will also try the chimney cap. Good luck.